I need help in breaking apart the orange squares to color each individually. I was following an online tutorial and the person clicked the Unite button which made the white crosses one piece (at the 42 seconds mark of this video) .When i did it, everything turned white.

Now as for what this presenter does with the Microsoft logo: he only selects the two white bars and then uses pathfinder unite on them. I don't know why he doesn't subtract them from the orange square, maybe he explains it in the video.